Plasma generator that creates local plasma using discharge of ignition plug and then enlarges this plasma using EM (Electro Magnetic) waves such as microwaves has been developed (see JP 2009-036198 A1). In this plasma generator, mixing circuit is provided for mixing the energy for discharging and energy of EM wave from EM wave generator. Mixing circuit is connected to an input terminal of the ignition plug. EM wave energy and high voltage pulses are thereby superimposed in a same transmission line and are supplied to the ignition plug. Ignition plug can therefore serve as both discharge electrode and EM wave radiating antenna.
However, the conventional plasma generator has a drawback for allocating a space for mixing circuit in a restricted space inside an engine because the mixing circuit is usually arranged on the ignition plug.